Electric switch



Oct. 16, 1951 R. GoLDscHMgDT ET AL 2,571,564

LECTRIC SWITCH Filed Jan. ll, 1949 3 SheeS-Shee l Inventos y MIKEL...

A ttorneys R. GOLDSCHMIDT ET AL oct. 16, 1951A ELECTRIC SWITCH 3 Sheets-Sheet 2 Filed Jan. ll, 1949 www/9770 Oct- 16, 1951 R. GoLDscHMlDT ET A1. 2,571,564

ELECTRIC SWITCH 5 Sheets-Sheet 5 Filed Jan. 1l, 1949 nvenlors llorneys Patented Oct. 16, 1951 UNITED STATES PATENT OFFICE ELECTRIC SWITCH British company Application January 11, 1949, Serial No. 70,222 In Great Britain January 14, 1948 (Cl. ZOO-80) 4 Claims. l

This invention relates to automatic electric switches in which mercury is employed within a rotatable container to make and break contact with electrodes through centrifugal action.

An object of this invention is to provide such switches which are of simple construction and which are particularly suitable for manufacture in small sizes.

The invention will now be more particularly described with reference to the accompanying drawings in which- Figure 1 is a part sectional side elevation on an enlarged scale of one form of automaticelectric switch mounted on a part of an electric generator incorporated in the hub of a pedal cycle Wheel.

Figure 2 is a diagrammatic front sectional view of the switch.

Figure 3 shows a modified form of electrode.

Figure 4 is a wiring diagram embodying the switch for lighting lamps on a pedal cycle.

Figure 5 is a diagrammatic sectional view on an enlarged scale of a Inodied form of automatic electric switch combined with a wiring diagram for lighting lamps on a pedal cycle.

Figure 6 is a fragmentary sectional view 0i the switch Shown in Figure 5 with the mercury displaced by centrifugal force.

Figure 7 is a vertical section showing a modification of the switch shown in Figs. 5 and 6.

Referring to Figures 1 and 2, the dotted line A-B indicates 'the axis of a cycle wheel whose hub is indicated at I. Fixed to the hub to rotate therewith is a steel ring 2 which forms part of an electric generator incorporated within the hub and the ring also constitutes a driving ring as hereinafter described. Contained within the hub is a plate 3 which is secured rigid with the wheel spindle, and forms part of the stationary armature of the generator. Also secured rigid with the spindle is a cover 4.

A substantially rectangular frame 5 made of insulating material is provided with holes to receive screws I for rigidly attaching the frame to the plate 3.

Secured to the frame for a purpose to be hereinafter described is a terminal 8. A terminal 9 is also secured to the frame and an electrical conductor I is connected at its one end to the terminal 9 and at its other end to one of two rivets II which secure the ends of a bifurcated blade spring I2 to the frame. Riveted to the spring I2 is a strap I3 and between the strap and spring is'rmly held a steel spindle I4. The spindle is formed with a flat I which abuts the spring 'and serves to prevent movement of the spindle relative to the spring so that good electrical and mechanical contact between the two parts .is assured. Integrally formed at the lower end of the spindle I4 is a head I6 against which abuts a brass bearing bush I1 of the so-called oilless type which is rotatably mounted on the spindle. The bush Il is secured by a drive-fit in a steel sleeve I8 the lower end of which forms an electrod@ 20. Formed on the exterior of the sleeve are screw-threads I9 and moulded to this part of the sleeve is an insulating plug 2l formed with screw-threads 22 which engage screwthreads in a hollow cylindrical or cup-shaped container 25 made of steel. The plug is formed with a tapered portion 23 and a shoulder 24 which co-operate with complementary parts on the container to eilect a good joint which is improved by means of a plastic or rubber solution at this place. The base 26 of the cup-shaped container is of shallow conical form, the apex` extending towards the interior of the container. A quantity of mercury 28 is enclosed in the c0n tainer which constitutes an electrode, and when the container is stationary the mercury occupies; a position as shown in Figure 2 making contact with electrode 20. Inside the container, adjacent the base is secured a split ring 21 made of steel and having its ends spaced apart a small amount sufficient to reduce the slip of the mercury against the container when the latter is made to rotate.

Slidably disposed in a groove in the frame 5 is a bolt 29 formed with a depending linger-piece 30 at one end and at its other end with an upstanding tongue 3l which projects into the cavity formed by the conical base 25. Also formed on the bolt 2'9 is a projection 32. A spring plate 33 is secured to the frame by screws 34 and has a slot 35 through which the tongue 3| projects and is bent at 36 to snap engage the projection 32. The front end 3l of the spring is also bent to provide a lead for the projection.

In the position shown in which the electrode 20 is immersed in the mercury the cycle wheel is stationary and the periphery of the container is spring pressed into frictional engagement with the driving ring 2. By rotating the wheel at an increasing speed the meniscus of the mercury gradually tends to ilatten until the mercury suddenly spills over the edge of the ring 21 into contact with the walls of the container and simultaneously recedes from the electrode 20. When the wheel de-celerates a speed is reached at which the mercury suddenly recedes from the walls of the container and simultaneously envelops the electrode 20 the mercury being then completely contained again within the ring 21. The split ring 21 therefore serves the dual purposes of providing a reduced effective diameter bore at that part of the container where the mercury rests when not under the action of centrifugal force, and of providing impeller means for reducing the slip of the mercury relative to the container during acceleration and retardation, the spaced apart ends of the ring 21 acting as a kind of keywayf To increase the impeller action the ring may be slotted. If it is desired to remove the container from contact with the driving ring 2 the bolt 29 is manually moved so that the tongue 3i abuts the bottom of the container and moves the container laterally against the action of the spring I2. By sliding the bolt until the projection 32 passes the front 31 of the spring plate 33 this position of the container can be maintained. y

In Figure 3 the sleeve I8, instead of having a co-axial electrode 2U, has an oiset electrode formed by an inclined face 43.

The switch may be used in a circuit for lighting lamps on a pedal cycle as shown diagrammatically in Figure 4. One output terminal of an electric generator 38 is earthed to the cycle frame and the other output terminal is connected to terminal 8 on the frame 5. The terminal 8 is also connected to one contact of the main lamp 39 in the cycle headlamp and the other contact of the lamp is earthed. One contact of a pilot lamp 42 is earthed and the other contact is connected to a switch ll which is connected to one poleV of a battery 4B. lThe other pole of the bat tery 4B is connected to the terminal 9 which is in permanent electrical connection with the contact 2B in the container 25.

When the cycle is stationary and it is desired that current should pass through the head lamp the switch'l is closed and the bolt 29 is moved to the position shown in Figure l, if it is not already in this position, so that the container is spring pressed into frictional and electrically conductive engagement with the driving ring 2 which Yconstitutes an earth Current can now pass through the pilot lamp 42. When the cycle is propelled the electric generator causes a current to pass through the main lamp 39 so that both lamps are illuminated until a predetermined speed is reached when the container 25 is rotating sufficiently fast to make the mercury 28 recede from the electrode 20 so that current ceases to pass through the lamp 42.

Referring now to Figures 5 and 6 the numeral 6| represents a driving ring rotatable with a cycle wheel and corresponding to part 2 in Figures 1 and 2. A hollow cylindrical container for a quantity of mercury /39 comprises a metal casing 5B closed at each end by screw-threaded plugs 5| made of insulating material. Each plug has a frusto-conical projecting portion 52 and the two portions converge one towards the other. Passing axially through the lower plug 5I is a metal rod l53 which projects at one end into the container toconstitute an electrode and at its other end 735 "the rod 54 constitutes a journal 56 which is fmounted in a bearing bush 58 supported in the '3315 Y the electrode 53.

frame 59. Connected to the bearing bush 58 is a metallic strip which is adapted to abut an earth contact 66. The frame 59 is supported in any convenient movable manner so that the container is adjustable laterally to one position in which it contacts the rotatable driving ring 6l and another position in which the strip 60 abuts the earth contact 65.

The switch may be connected in a lighting circuit for a pedal cycle in the following manner. The circuit comprises a pair of lamps 62 connected in parallel and earthed to the cycle frame. The lamps are also connected to a hand switch 63 connected to an electric generator 64 and a battery 65. The generator is connected to the upper bearing bush' 58 and the battery is connected to the lower bearing bush 51.

The operation of the circuit is as follows considering the cycle to be stationary. With the hand switch 63 in the position as shown and the container in frictional contact with the rotatable sleeve 6l the battery supplies current to the lamps through the switch in which the mercury contacts the electrode 53 and the casing 5D which is earthed. When the cycle is propelled and the container thereby rotated at an accelerating speed the shape of the mercury `gradually changes and, at a pre-determined speed, makes contact with the rim of the electrode E55 and recedes from In this position, which is clearly shown in Figure 6, the generator is switched into circuit with the lamps and the battery is switched out of circuit. When it is desired to rely solely on the generator, contact between the container and the driving ring BI is broken by lateral movement of the frame 5S and contact between the strip 3G and the earth 56 is made.

The container may have a reduced diameter bore in which the mercury is contained when the container is stationary and this may be eiected by a split ring 21a similar to that described with reference to Figures l and 2. The ring would, of course, also serve as an impeller for the mercury.

In the switches above described the container is adapted to be vrotated by frictional engagement of its periphery with a driving ring and the engagement is also used for the conduction of an electric current. If the container has a hard surface and the driving ring also has a hard surface such as is produced by chromium plating the mechanical as well as the electrical contact between the two surfaces is imperfect. To avoid these disadvantages the container is provided with a metallic surface of good conducting material which is softer than the driving ring. Nickel, copper or cadmium or other metals may be employed and may be provided on the container by electro-deposition.

To improve the reliability of the switch by reducing the liability to oxidation in the mercury may be immersed in a non-oxidisable or a not easily oxidisable liquid immiscible with mercury. Oils are particularly suitable liquids so long as those which do not have harmful effects on mercury are chosen. Oils containing free sulphur or which are liable to give off sulphur should be avoided. Transformer oils and oils for use in oil-switches have been found to be suitable. An important result is that the oil does not affect the electric contacting unfavourably, the pressure exercised by the mercury being so great that it pushes the oil aside` at the moment of contacting.

As beforestated the electrodes are made from steel or' iron vor other conducting material which does not easily form an amalgam, and are provided on their mercury-contacting surfaces with a layer of amalgam-forming metal, so that formation of an amalgam is limited to this layer. The amalgam may be formed by treatment prior to assembly of the switch. The amalgam forming metal preferably employed is copper, although other metals such as silver may be employed, and may be provided on the electrodes by electrodeposition. In some cases it may be convenient or desirable to deposit a small spot or spots of the amalgam forming metal on a very small area of an electrode, preferably opposite another electrode.

It should be appreciated that the design of an automatic electric switch to be operated by the wheel of a pedal cycle to control a lighting circuit or circuits on the cycle is governed by various considerations. For example the switch must be sufficiently robust to enable it to withstand hard wear, vibrations, and rough treatment which may extend over prolonged periods, but also the switch must be small, simple, inexpensive and constructed to withstand bad Weather and dusty conditions which are accentuated by the proximity of the switch to the cycle wheel. In this connection therefore it is essential that the make and break parts of the switch be completely sealed and that no slip rings and brushes are employed for conducting the current to and from the switch. In the case of a cycle having incorporated an electric generator within the hub of a wheel and such an automatic centrifugal mercury switch for closing a battery circuit at low speeds, the centrifugal forces of the mercury at the speeds at which the switch makes and breaks are low compared with gravitational forces so that the switch may, if not correctly designed, suffer from undesirable sensitivity. All these considerations make it obvious that the solution of the problem to design a satisfactory automatic electric switch for a pedal cycle is a diiiicult one.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. An automatic electric switch comprising a container having a wall made of metal adapted for frictional 'driving engagement on its outer surface, electrically conductive bearing means at each end of the container electrically insulated from the metal wall and adapted to support the container for rotation about a substantially vertical axis, a quantity of mercury within the container in constant electrical contact with the metal wall thereof, an electrode projecting upwardly into the container coaxially therewith and connected electrically with the lower bearing means, and an electrode which depends into the container and is disposed between the metal wall thereof and the upwardly projecting electrode and is connected electrically to the upper bearing means, whereby when the container is stationary or rotating at low speeds the mercury contacts the upwardly projecting electrode but not the depending electrode, and when the container is rotating at higher speeds the mercury, under the action of centrifugal force, contacts the depending electrode but not the upwardly projecting electrode.

2. An automatic electric switch comprising a container having a wall made of metal adapted for frictional driving engagement on its outer surface, an electrically insulating closure member secured to the upper end of the container, a

quantity of mercury within the container in constant electrical contact with the metal wall thereof, an electrode comprising an electrically conductive sleeve secured in and depending from the closure member co-axially with the container and closed at its lower end to contact the mercury, bearing means including an electrically conductive bearing bush secured rigidly within said sleeve and the container and electrically connected to said sleeve but electrically insulated from the container wall, and a non-rotatable electrically conductive bearing spindle co-axial with the container and having means for supporting it and on which said bush is supported and maintained rotatably to support the container and allow it to rotate about a substantially vertical axis, said depending electrode sleeve being electrically connected to and co-axial with said bearing bush, whereby the mercury under the action of centrifugal force makes and breaks oontact with the lower closed end of `said electrode sleeve at predetermined speeds of rotation of the container to make and break the circuit between the bearing means and the wall of the container.

3. An automatic electric switch in accordance with claim 2, wherein the supporting means for said bearing spindle comprises an electrically conductive blade spring connected to the spindle in an electrically conductive manner, and a rigid frame to which the blade lspring is attached.

4. An automatic electric switch comprising a container having a wall made of metal adapted for frictional driving engagement on its outer surface, bearing means including a non-rotatable bearing member co-axial with the container, and a complementary bearing member rigid with but electrically insulated from the container wall and rotatably mounted on the non-rotatable bearing member to support the container and allow it to rotate about a substantially vertical axis, a quantity of mercury within the container in constant electrical contact with the metal wall thereof, a depending electrode electrically connected to and co-axial with one of the bearing members, whereby the mercury under the action of centrifugal force makes and breaks contact with the electrode at predetermined speeds of rotation of the container to make and break the circuit between the bearing means and the wall of the container, means to support the container for movement laterally, resilient means to urge the container in one direction laterally, and means to maintain the container in position against the action of the resilient means.

RUDOLF GOLDSCHMIDT. ALBERT lEDWARD WOOD.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 182,977 Weston Oct. 3, 1876 949,859 Swift Feb. 22, 1910 1,041,594 Claudon Oct. 15, 1912 1,954,019 Moore Apr. 10, 1934 2,164,991 Ingress July 4, 1939 2,233,900 Rowe Mar. 4,1941 2,299,762 McDermott Oct. 27,1942 2,414,836 Rickmeyer Jan. 28, 1947 FOREIGN PATENTS Number Country Date 14,928 Great Britain Sept. 24, 1892 

